This program of research focuses on aging-related changes in cognition and health, and in explaining cognitive change in the context of health and health-related change (i.e., morbidity, comorbidity). A key objective is to identify processes of change other than chronological age (i.e., simple passage of time) that account for population and individual-level change in cognitive functions. Identification of processes of change will proceed through detailed consideration of within-person change in health indicators (morbidity and comorbidity) and patterns of change prior to death. Contributions to theory include focused attention on health as a causal factor in aging-related changes and the role of sociodemographic and psychosocial influences in predicting changes in health and moderating the health-cognitive link. Using a within-person perspective, strong tests will be made of psychological theories of cognitive aging (speed and sensory mediation, common cause), developed primarily on the basis of age differences. Methodological features include inference to defined populations of aging individuals conditional on mortality-selection, multivariate analysis of correlated and coupled change, estimation of change-points, and cross-national generalizability. This project brings together multidisciplinary teams of investigators from 21 longitudinal studies on aging. A coordinated and collaborative approach to the integrative understanding of aging, health, and cognition will lead to significant gains in knowledge from these longitudinal studies and permit the identification and reconciliation of differences found across studies in terms of measurement, sampling, demographic, social, and health indicators. This broad collaboration has extensive multidisciplinary expertise and interdisciplinary interests. The diversity of perspectives is maintained in the development of analysis protocols, ensuring generalizability of results and evaluation of the sensitivity of results to decisions regarding measurement harmonization, analysis, and choice of theoretical models, while maximizing data value from each study. The findings from this research program will provide a basis for prevention and intervention efforts and inform health policy by identifying premorbid and subsequent changes associated with morbidity and comorbidity, and sociodemographic and psychosocial moderators of these changes. Potential interventions will be enhanced by early identification of change-points signaling subsequent loss of function and mortality.